1. Field of the Invention
The present invention relates to a device for supplying at a constant flow rate a fluid utilizing apparatus, for example a spray gun, with at least one fluid having a variable viscosity, for example paint, comprising a fluid source delivering said variable viscosity fluid and a fluid circuit connecting said fluid source to the fluid utilizing apparatus.
2. Description of the Prior Art
A paint spray gun is generally supplied with paint by a supply source delivering paint under pressure. The paint leaves the gun through a nozzle which may be sealed by a needle. The needle is for stopping or enabling the paint flow. Furthermore, a partial opening in the needle allows the flow to be adjusted by constricting to a greater or lesser extent the passage through the nozzle.
Such a conventional system is simple, but it does not allow a constant paint flow rate to be obtained. To obtain this constancy, it would be necessary first of all to accurately adjust the supply pressure for the paint, which could possibly be effected with a pressure reducer. But that would not be sufficient, for the flow rate of the paint through the orifice of the nozzle depends on the viscosity of the paint. Now, the viscosity of the paint is variable with the quality thereof, its dilution and especially its temperature. It will be readily understood that it is difficult to have the temperature absolutely under control.
According to the quality and the dilution of the paint, the pressure and the opening of the needle could be adjusted to the desired value, depending on the flow rate, but, for numerous uses, the paint is frequently changed during the working day to change the colour thereof for example. It would therefore be necessary, for each change, to adjust the pressure or the opening of the needle.
Furthermore, it is difficult to measure the paint flow rate, for the simple flow rate measuring systems give readings varying with the viscosity.
Finally, paints are abrasive and the wear of the orifices of the nozzles or of the ends of the needles causes variations in flow rate.
It is therefore of the most interest to supply a paint spray gun not with a constant pressure, but with a constant flow rate. It is certain, in this case, that the paint pressure may vary with all the elements mentioned above, but the constancy of the paint pressure is not required to ensure proper operation of the gun.